Modern computers are frequently equipped with multiple peripheral devices with which the computers communicate. These devices include, for example,
printers and plotters; PA1 communication devices, such as telephone modems and video conferencing expansion cards; PA1 pointing devices such as digitizing pads and mouses; and PA1 storage media, such as disc drives and tape drives.
Many computers are based on a single-bus architecture. One example is the so-called "personal computer," which was developed by IBM Corporation, Armonk, N.Y., and which is designed around the 8XX86 series of microprocessors manufactured by INTEL Corporation, Santa Clara, Calif. The single bus is used for communication between the computer's microprocessor and the devices described above.
However, the single bus can sometimes act as a bottleneck, since only a single agent at any time can use the bus for communication. For example, during a printing task the bus is occupied, because the microprocessor sends the data to a printer, using the single bus. An incoming message, as from a telephone modem, will generally be blocked from the bus, and must wait for release of the bus by the processor. Further, the blockage can occur, no matter how important the incoming message may be, relative to that of the printing task.